One hundred and four patients with multiple primary malignant neoplasm (MPN) with at least one genitourinary organ involved were analyzed. The 104 patients represented 0.9% of all cancer patients and 9.0% of all urologic tumor cases. Tumors of the prostate and bladder in urologic cancers and tumors of the gastrointestinal tract, particularly stomach cancer, in non-urologic cancers were predominantly involved. In 79 cases (76.0%), the second tumors were discovered within 5 years from the diagnosis of the first cancer. Renal cell carcinoma tended to be discovered incidentally and concomitantly. In contrast, bladder cancer tended to be an initial primary tumor presenting with symptoms, and tumor of prostate tended to be found incidentally, as a second cancer in metachronous cancer associations. All second tumors of the liver were found incidentally with ultrasonographic examination after a small interval. Strict follow-up at regular intervals at least the initial 5 years are essential for the detection of second malignant neoplasms.